Television method



Sept. 27, 1938. M. voN ARDENNE 2,131,203

TELEVISION METHOD Filed May 16, 1932 MEE/@1 E EM Patented Sept. Y27,1938 UNITED STATES PATENT `QFFECE TELEVISION METHOD Application May 16,V1932, Serial No. 611,568 In Germany March 27, 1931 1 Claim.

In the television art there is frequently made use of cathode ray tubesfor transmitting images or optical occurrences as Well as forreproducing in the receiver the transmitted images.

In both cases the cathode ray produced in the tube is deilected by meansof deflecting systems which may consist of deflecting plates or ofdeliecting coils. The deflection of the ray is effected by applying tothe deiiecting systems defleeting voltages of an apt Wave form as toscan the fluorescent screen of the tube. The cathode ray which isprojected onto the screen in the form of a luminous spot scans an area,which with `correctly selected deecting voltages appears in the form ofan evenly luminous rectangle on the fluorescent screen of the tube.

An extraordinary improvement was obtained by the introduction of the newthin, very even and extremely sensitive screen. It was possible with thenew screen, with an anode potential amounting to 2300 volts and acurrent of 0.87 milliampere to obtain on the outside of the tube a pointbrightness of approximately 1.2 candle power.

But there exists the diiculty that the sensitive screen may be damagedby the cathode ray at any point Where the cathode ray remainsstationary, which is the case when a cathode ray impinges on theluminous screen and the de- 30 iiecting voltages are failing.

The present invention, now, is based on the following considerations:

In order to prevent burning of the sensitive screen material it is ofgreat importance for avoiding this difficulty to provide means whichprevent the beam from occasionally remaining stationary.

Generally speaking, this invention accordingly has for its object toprovide to cut oi the cathode o ray when the deecting voltages fail.

In most cases the danger of a portion of the screen being damaged willbe eliminated by taking care that at least one of the deflectingoscillations is maintained as long as a cathode 5 ray is allowed toimpinge on the fluorescent screen, or in other words, that the ray isprevented from impinging on the screen as soon as both deiiectingoscillations cease.

This may be accomplished, for example, by

o means of a relay or the like, cutting 01T the anode potential, orapplying to the Wehnelt cylinder a biasing potential of such nature thatemission through the anode is not longer able to take place.

The novel features which are believed to be characteristic for theinvention are set forth with particularity in the appended claim. Theinvention, however, may be best understood by reference to the followingdescription taken in 5 connection with the accompanying Figs. 1 and 2which show exemplary schematic arrangements of the invention.

To Figs. 1 and 2 there is common a Braun tube I with a fluorescentscreen 2, a cathode 3, a 10 Wehnelt cylinder 4, an anode 5, a rst pairof deilecting plates 6 connected to a frame frequency generator 8, asecond pair of deflecting plates 'I connected to the line frequencygenerator 9, two rectifier devices I0 and II, two relays 15 arrangementsI2 and I3, an anode battery I5 and a cathode heater battery I6. Inparticular in Fig. 1 there is provided a strong negative bias battery I4which is lying between the cathode 3 and the Wehnelt cylinder 4 over theserially connected rest-contacts I 'I and I8 of the relay. The windingsof the relays are connected to the frame frequency generator 8 and theline frequency generator 9 respectively. When a generator is inoperation, a direct current will ilow 25 via the respective rectier andrelay winding so that the respective contact is opened. Consequently,when both deiiecting potential generators fail to operate, the negativebias of I4 is applied between cathode and Wehnelt cylinder, so that nocathode ray is allowed to pass through the anode aperture.

According to Fig. 2, relays and rectiers are disposed like in Fig. 1,with the exception that the contacts open, when both deecting generatorsare failing, so that the high anode potential |5 of the Braun tube isdisconnected and no cathode ray is allowed to impinge the screen.

I claim:

In a television arrangement comprising a cathode ray tube havingcathode, anode, deecting system and a fluorescent screen, a source ofhigh tension direct current connected to said cathode and anodeproducing the cathode ray, and a source of variable current connected tosaid deecting system, a relay the primary side of which is connected tosaid source of variable current and the switch of which interrupts thehigh tension current so as to prevent the cathode ray to burn saidfluorescent screen when said variable current ceases.

MANFRED VON ARDENNE.

